Field of the Invention
The present disclosure relates to a toner, a toner stored unit, an image forming apparatus, and an image forming method.
Description of the Related Art
Heretofore, a latent image that is electrically or magnetically formed is visualized with an electrophotographic toner (may be referred to simply as a “toner” hereinafter) in an image forming apparatus of an electrophotographic system etc.
Recently, market demands for high-speed operations and energy saving of image forming apparatuses have been getting strong. There is a need for a toner that has excellent low-temperature fixing ability and can create high-quality images. In order to achieve low-temperature fixing ability of a toner, a softening temperature of a binder resin of the toner needs to be low. When the softening temperature of the binder resin is low, however, so-called offset (also referred to as hot offset hereinafter) tends to occur. The offset is a phenomenon where part of a toner image is deposited on a surface of a fixing member during fixing and the deposited toner is transferred to a copy sheet. Moreover, heat resistant storage properties of the toner deteriorate and so-called blocking where toner particles are fused to each other occurs especially in a high-temperature environment. Also there are problems caused inside the developing device, such as a problem where the toner is fused on the inner area of the developing device or a carrier to contaminate, and a problem where the toner is easily filmed on a surface of a photoconductor.
As a technique to solve the above-described problems, known is use of a crystalline resin as a binder resin of a toner (see, for example, Japanese Patent Nos. 3949553 and 4155108). Since the crystalline resin has properties that a state of the crystalline resin sharply soften at a melting point from a crystalline state, the crystalline resin can significantly reduce a fixing temperature of the toner. Although low-temperature fixing ability of a toner is improved, the toner is soft and easily causes plastic deformation when the crystalline polyester and amorphous polyester are merely blended. Specifically, heat resistant storage properties of the toner become poor, and the toner cannot be supplied because the toner particles are aggregated inside a toner stored container and an image forming apparatus. As a result, the toner density decreases and defective images may be formed. Since it takes a time to recrystallize the crystalline resin inside a toner after the toner is melted on a fixing medium by heat fixing, moreover, hardness of a surface of an image cannot be recovered quickly. As a result, there are problems that scratch marks may be formed on a surface of an image by contact and abrasion with a paper ejection roller or conveying member during a paper ejection step after fixing, and copy sheets are adhered (image adherence resistance) to each other when a large volume is printed.